1. Field of the Invention
The present invention relates to a curing device used, for example, in a semiconductor manufacturing apparatus.
2. Prior Art
Lead frames to which chips have been die-bonded with a paste are heated in a curing device so that the paste is hardened.
In such a curing device, the heating of the paste generates gases that can cause contamination. These gases flow around the edges of the chips and stick to the chip surfaces in a solid or gaseous form, which eventually could affect the performance of the chips. The gases can also adhere to the surface of heater blocks that are used in the curing device; and if this happens, then the lead frames stick to the heater block.
Conventionally, the contaminant gases are removed by blowing an inert gas, a reducing gas, etc., onto the chips from above. The gas flows around the edges of the chips and then escapes out of the curing device.
This type of method is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 63-239957 and 63-316443. However, the problem of the lead frames sticking to the heater block cannot be completely solved by this method alone.
One method to prevent the lead frames from sticking to the heater block is disclosed in, for example, Japanese Utility Model Laid-Open No. 2-8033. In this method, minute projections which run continuously in the direction in which the lead frames are conveyed are formed on the upper surface of the heater block, and the lead frames are kept above the surface of the heater block with a space in between.
However, in the method described above, the upper surface of the heater block needs to be worked on to form the projections. In addition, the manufacturing and finishing processes of the heater blocks with the projections are difficult and costly. Furthermore, it is impossible to treat all the different types of lead frames always evenly on the projections of the heater block.
More specifically, depending on the number and positions of the chips mounted on each lead frame, the projections of the heater block could be located directly beneath the chips. If this occurs, not all the chips are maintained at a thermally constant distance from the upper surface of the heater block.
In addition, if the chip parts mounted on the lead frames form "islands" (in other words, if the chip parts project downward), the lead frames of the chip parts would be inclined and positioned where the projections on the heater block are located. In this case, it cannot be assured that all the chips are maintained at a constant distance, in terms of heating temperature, from the upper surface of the heater block.
As a result of these problems, in the past, a multiple number of heater blocks are required (one for each type of lead frame to be handled). Furthermore, because of the presence of the projections on the heater block that extend in the feeding direction of the lead frames, the gases between the lead frames and the heater block can only flow in the feeding direction of the lead frames. Thus, the gas discharge efficiency tends to be poor.